Chem Exam 1

What are properties of solids?

Retains own shape and volume, does not expand, does not flow, particles essentially in fixed positions closed together

What are the properties of gas?

Assumes the volume and shape of container, readily expands, flows with freedom of motion, particles farther apart

What are the properties of liquid

Assumes shape of the container, not voume. Does not expand. Flows readily but still close. Particles closer together.

Define intermolecular forces

attraction between water molecules.

Weaker than intramolecular forces

Forces that hold atoms together within a molecule such as covalent bonding.

If the intermolecular forces increase, what happens to the melting point of a solid?

Solid A has greater intermolecular forces than solid B. The stonger the intermolecular forces, the more the particles in the solid are held together. This means we need more energy to "free" the particles from their fixed positions. So the melting point of solid A is greater than solid B.

In other words the greater the intermolecular forces, the greater the melting point or boiling point of a substance.

Define London Dispersion

influenced by increasing molar mass and molecular shape

present in all molecules

weakest force, but may contribute the most

define dipole-dipole

results from attraction between polar molecules

the greater the polarity, the greater this force

define Hydrogen bonding

a form of dipole dipole interaction

results when hydrogen is bonded to f, o, n

define ion dipole

for mixtures only and not for pure substances

mixtures of ionic and polar compounds

define mp

melting point

define bp

boiling point

T/F - the more IM forces we have, the higher BPand MP.

TRUE

define enthalpy of fusion

heat energy used to change between a solid and a liquid

define enthalpy

a measure of the total heat energy of a system at constant pressure.

define enthalpy of vaporization, ΔH_vap

The heat energy used to change between a liquid and a gas

How is enthalpy measured?

In kj/mol

Which is greater, enthalpy of fusion or enthalpy of vaporization?

The enthalpy of vaporization is greater. It takes more energy to form a vapor (particles move very fast in the vapor phase and are far apart) than it does to allow the particles to flow but still stay close together in a liquid.

Where does energy go when its melting from a solid to a liquid?

It goes to breaking the IM forces that hold the solid together

Where does energy go when its boiling from a solid to a liquid?

It goes to breaking the IM forces that hold the liquid together

Changing from solid to vapor is a

Endothermic process